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At least 145 records · Page 8Linked to original sources
USGS2007

Further assessment of environmental contaminants in avian prey of the peregrine falcon in big bend National Park, Texas

A small resident population of peregrine falcons (Falco peregrinus anatum) in the Big Bend region of Texas has suffered reproductive failures since 1990. To continue our assessment of the effects of environmental contaminants on the peregrine falcon, we collected representative avian prey species during 2001 at Mariscal Canyon, Big Bend National Park. The avian carcasses were analyzed for inorganic and organochlorine contaminants. Concentrations of Se and Hg were present at high levels (up to 11 and 2.2 ??g/g dry weight, respectively) in some avian prey and could be implicated in reproductive failures of the peregrine falcon in Big Bend National Park. All other inorganic elements were below concentrations known to affect reproduction or to be associated with other deleterious effects in birds. Of all the organochlorines analyzed, only DDE and total PCBs were present above detection limits in all species, although at low concentrations. Our study provides further support to the hypothesis that contaminants in potential avian prey of the peregrine falcon in the Big Bend region are implicated in the productivity failures observed in this species since 1990.

Southwestern Naturalist↗
USGS2007

Effects of methylmercury on reproduction in American kestrels

Sixty breeding pairs of captive American kestrels ( Falco sparverius ) were exposed to a range of sublethal dietary concentrations of mercury (Hg), in the form of methylmercuric chloride, and their subsequent reproduction was measured. Egg production, incubation performance, and the number and percent of eggs hatched decreased markedly between 3.3 and 4.6 mg/kg dry weight of Hg (1.2 and 1.7 mg/kg wet wt), in the diet. The number of fledglings and the percent of nestlings fledged were reduced markedly at 0.7 mg/kg dry weight (0.3 mg/kg wet wt) and declined further between 2 and 3.3 mg/kg dry weight (0.7 and 1.2 mg/kg wet wt). Dietary concentrations of ⩾ 4.6 mg/kg dry weight (1.7 mg/kg wet wt) were associated with total fledging failure. The estimated decline in fledged young per pair (24%, Bayesian regression) for kestrels consuming 0.7 mg/kg dry weight (0.3 mg/ kg wet wt) raises concerns about population maintenance in areas subject to high inputs of anthropogenic Hg. Mercury concentrations in 20 second-laid eggs collected from all groups were related to dietary concentrations of Hg, and the Hg concentrations in 19 of these eggs were related to eggs laid and young fledged. Concentrations of Hg in eggs from the highest diet group (5.9 mg/kg dry wt; 2.2 mg/kg wet wt) were higher than egg concentrations reported for either wild birds or for captive birds (nonraptors) fed dry commercial food containing 5 mg/kg methylmercury. Accumulation ratios of Hg from diets to eggs were higher than those reported for feeding studies with other species.

Environmental Toxicology and Chemistry↗
USGS2007

Bayesian multimodel inference for dose-response studies

Statistical inference in dose-response studies is model-based: The analyst posits a mathematical model of the relation between exposure and response, estimates parameters of the model, and reports conclusions conditional on the model. Such analyses rarely include any accounting for the uncertainties associated with model selection. The Bayesian inferential system provides a convenient framework for model selection and multimodel inference. In this paper we briefly describe the Bayesian paradigm and Bayesian multimodel inference. We then present a family of models for multinomial dose-response data and apply Bayesian multimodel inferential methods to the analysis of data on the reproductive success of American kestrels (Falco sparveriuss) exposed to various sublethal dietary concentrations of methylmercury.

Environmental Toxicology and Chemistry↗
USGS2019

Community-based conservation and recovery of native species on Monuriki Island, Fiji

The small uninhabited island of Monuriki (40.4 ha) in western Fiji is of national and international conservation concern for its several protected species. Exotic invasive species and a Category 5 cyclone have exacerbated conservation challenges. The cooperation of local, national, and international stakeholders continues to be crucial in restoration of the island’s native flora and fauna. This summary presents a timeline of restoration efforts and current status of the recovery programme for Monuriki. The critically endangered dry forest habitat of Fiji is only found in a few isolated patches on disparate islands. The Fijian crested iguana (Brachylophus cf. vitiensis) is a critically endangered species restricted to a few small islands in this dry forest zone of western Fiji. The population of crested iguanas on Monuriki Island is the third largest remaining population. Even before iguanas were first documented on the island in the early 1980s, individuals had been removed by local resorts for display purposes, a practice that was previously unregulated. In the late 1990s, the first efforts to conserve and restore Monuriki Island were discussed, but conservation initiatives were not implemented until the development of the Crested Iguana Recovery Plan in 2008. In 2011, domestic goats (Capra hircus) and non-native rats (Rattus exulans) were removed from the island, and 10 pairs of iguanas were brought into captive breeding facilities within Fiji. In 2015, the first 32 captive-bred crested iguanas were released back on Monuriki Island. More than half of these iguanas (N=26) were radio-tracked for 56 days post-release in order to assess survivorship and help provide insights into their short-term movement patterns. Of the 26 iguanas that were tracked, nearly 70% (N=18) were found after 56 days indicating excellent short-term survival. In February 2016, Tropical Cyclone Winston, a Category 5 storm passed through Fiji and devastated some of the tropical dry forest habitat on Monuriki. With sustained winds of up to 230 km/ hr nearly all of the canopy leaves from trees on Monuriki Island were removed and large amounts of debris covered the forest floor. Following the cyclone, a brief wildlife survey revealed Monuriki’s iguana and bird populations were still present. In 2017, the crested iguana captive breeding programme was brought to an end when 16 of the original 20 iguana founders, and an additional 32 captive bred off spring, were reintroduced onto Monuriki. This was accomplished, in part, due to successful breeding and reestablishment of the remaining wild iguanas on the island. Despite a major storm event, reestablishment likely resulted from reduced egg and hatchling predation by the rats, and excellent habitat recovery after goat removal. Overall these invasive species eradications have proven highly successful for the recovery of the iguanas, wedge-tailed shearwaters (Puffi nus pacifi cus), and several other non-target species including the banded rail (Gallirallus philippensis) and endangered Fijian peregrine falcon (Falco peregrinus). Furthermore, eradication of non-native species has also helped the recovery of the highly threatened tropical dry forest ecosystem in which these species exist.

Monuriki island↗
USGS1997

The influence of habitat, prey abundance, sex, and breeding success on the ranging behavior of Prairie Falcons

We studied the ranging behavior and habitat selection of radio-tagged Prairie Falcons (Falco mexicanus) during the breeding season in southwestern Idaho. The distribution and numbers of Townsend's ground squirrels (Spermophilus townsendii), the primary prey of Prairie Falcons in our study area, varied in response to drought during the study period. Prairie Falcons ranged over large areas (ca. 300 km2) and increased their foraging ranges in response to declining ground squirrels. Reptiles and birds were preyed upon most frequently when squirrels were rare. Males and females differed little in their use of space. Successful pairs ranged over smaller areas than non-nesters and unsuccessful pairs. Falcons nesting near habitat most suitable for ground squirrels ranged over smaller areas than those nesting farther from such habitat. Home ranges contained significantly more winterfat (Ceratoides lanata) and native perennial grasses (especially Poa secunda), and significantly less salt desert shrubs and exotic annual grasses than expected based on availability. Salt desert shrubs were found less than expected, based on availability in core areas within home ranges. Selection for winterfat and bluegrass in core areas was contingent upon selection at the larger scale of the home range; falcons with home ranges containing more winterfat and bluegrass than expected based on availability were less selective in their placement of core areas with respect to these habitats. We believe salient features of Prairie Falcon home ranges result largely from patchy distribution of landscape features associated with different densities and availabilities of Townsend's ground squirrels.

The Condor↗
USGS1981

Decline and present status of breeding Peregrine Falcons in Oregon

Unprecedented declines of the Peregrine Falcon ( Falco peregrinus ) throughout much of the Northern Hemisphere became apparent during the Madison Peregrine Falcon Conference in 1965 (Hickey 1969). Data from Britain were the most detailed; broken or missing eggs were much more common in 1949-56 than they had been in earlier years (Ratcliffe 1958). Subsequently, Ratcliffe (1967) showed a significant decrease in eggshell weight of peregrines in Britain starting in 1947 or 1948. Later, the same finding was demonstrated in North America (Hickey and Anderson 1968). The relation of eggshell thickness to DDE residue levels was established for Alaskan peregrines by Cade et al. (1971) and Peakall et al. (1975). Peakall (1976) stated that pesticides were considered to be a major factor in the decline of the peregrine, and tentatively concluded that the level of DDE in eggs that failed to hatch was 15-20 ppm (wet weight.)

Oregon↗
USGS1996

DDE decreases in plasma of spring migrant peregrine falcons, 1978-94

Mean p,p'-DDE (DDE) residues in plasma of combined adult and subadult female peregrine falcons (Falco peregrinus) decreased significantly in spring migrants captured at Padre Island, Texas, between 1978 and 1979 (1.00 μg /g wet wt), 1980 (0.57), 1984 (0.50), and 1994 (0.34). No other organochlorine pesticides were detected (detection limit, 0.02 μ g/g) in 1994. Mirex, oxychlordane, dieldrin, heptachlor epoxide, and the parent material DDT were routinely found in plasma samples in earlier years. Polychlorinated biphenyls (PCBs) were found in 75% of the adult females in 1994, but PCB data collected in 1984 were not comparable. The decrease in organochlorine pesticide residues was associated with peregrine population increases in the Arctic and elsewhere in North America. The arctic peregrine ( F. p. tundrius ) was removed from the list of Threatened and Endangered Species by the U.S. Fish and Wildlife Service in 1994. Satellite telemetry and plasma sampling provide new insight into continuing sources of DDE and PCBs. Chemicals that replaced organochlorine pesticides require additional investigation in North and South America.

Texas↗
USGS1983

Effects of heptachlor on American kestrels in the Columbia Basin, Oregon

Wheat seeds treated with heptachlor to control wireworms (Ctenicara pruinina) resulted in American kestrels (Falco sparverius) in the Columbia Basin accumulating residues of heptachlor epoxide (HE) that reduced productivity and caused some adult mortality. The kestrel is more sensitive to HE residues in eggs than the Canada goose (Branta canadensis moffitti), i.e., reduced productivity occurs at > 1.5 ppm in kestrel eggs vs. > 10 ppm in Canada goose eggs. Neither kestrel eggshells nor Canada goose eggshells were thinned by HE. The reduced use of heptachlor in 1979, because of a partial ban, resulted in an immediate lowering of HE concentrations in kestrel eggs the following year.

Oregon↗
USGS1990

Habitat relationships and nest site characteristics of cavity-nesting birds in cottonwood floodplains

We examined habitat relationships and nest site characteristics for 6 species of cavity-nesting birds--American kestrel ( Falco sparverius ), northern flicker ( Colaptes auratus ), red-headed woodpecker ( Melanerpes erythrocephalus ), black-capped chickadee ( Parus atricapillus ), house wren ( Troglodytes aedon ), and European starling ( Sturnus vulgaris )--in a mature plains cottonwood ( Populus sargentii ) bottomland along the South Platte River in northeastern Colorado in 1985 and 1986. We examined characteristics of cavities, nest trees, and the habitat surrounding nest trees. Density of large trees (>69 cm dbh), total length of dead limbs ≥10 cm diameter (TDLL), and cavity density were the most important habitat variables; dead limb length (DLL), dbh, and species were the most important tree variables; and cavity height, cavity entrance diameter, and substrate condition at the cavity (live vs. dead) were the most important cavity variables in segregating cavity nesters along habitat, tree, and cavity dimensions, respectively. Random sites differed most from cavity-nesting bird sites on the basis of dbh, DLL, limb tree density (trees with ≥1 m dead limbs ≥10 cm diameter), and cavity density. Habitats of red-headed woodpeckers and American kestrels were the most unique, differing most from random sites. Based on current trends in cottonwood demography, densities of cavity-nesting birds will probably decline gradually along the South Platte River, paralleling a decline in DLL, limb tree density, snag density, and the concurrent lack of cottonwood regeneration.

Journal of Wildlife Management↗
USGS1990

Recent trends in counts of migrant hawks from northeastern North America

Using simple regression, pooled-sites route-regression, and nonparametric rank-trend analyses, we evaluated trends in counts of hawks migrating past 6 eastern hawk lookouts from 1972 to 1987. The indexing variable was the total count for a season. Bald eagle ( Haliaeetus leucocephalus ), peregrine falcon ( Falco peregrinus ), merlin ( F. columbarius ), osprey ( Pandion haliaetus ), and Cooper's hawk ( Accipiter cooperii ) counts increased using route-regression and nonparametric methods (P < 0.05). Northern harrier ( Circus cyaneus ) counts increased based on the nonparametric method (P < 0.01) but not the route-regression method (P > 0.10). We found no consistent trends (P > 0.10) in counts of sharp-shinned hawks ( A. striatus ), northern goshawks ( A. gentilis ) red-shouldered hawks ( Buteo lineatus) , red-tailed hawks ( B. jamaicensis ), rough-legged hawsk ( B. lagopus ), and American kestrels ( F. sparverius ). Broad-winged hawk ( B. platypterus ) counts declined (P < 0.05) based on the route-regression method. Empirical comparisons of our results with those for well-studied species such as the peregrine falcon, bald eagle, and osprey indicated agreement with nesting surveys. We suggest that counts of migrant hawks are a useful and economical method for detecting long-term trends in species across regions, particularly for species that otherwise cannot be easily surveyed.

Michigan, Minnesota, New Jersey, New York, Pennsyl↗
USGS2018

Incorporating productivity as a measure of fitness into models of breeding area quality of Arctic peregrine falcons

Using empirical location data from individuals to model habitat quality and species distributions is valuable towards understanding habitat use of wildlife, especially for conservation and management planning. Incorporating measures of reproductive success or survival into these models helps address the role of vital rates (a surrogate of fitness) in affecting a species’ distribution. We used 24-year datasets of Arctic peregrine falcon ( Falco peregrinus tundrius ) nest-site locations and productivity from the Colville River Special Area, Alaska, USA to model suitability of breeding habitat and the relative quality of used and potential nest sites. We used zero-inflated negative binomial regression models and covariates describing nest-site productivity, area of surrounding prey habitat, geology, topography, and land-cover type to model and predict intensity of Arctic peregrine falcon nest-site use along the Colville River, and developed a predictive map of intensity of nest-site use. Regions of higher predicted intensity of use were characterized by steeper slopes, greater area of prey habitat, and higher average productivity, which are likely attributed to minimizing predation risk, gaining advantages for hunting, having sufficient prey resources, site quality, and overall fitness. Including productivity in intensity of nest-site use models improved the models, supporting our supposition that adding a fitness parameter enhanced the predictive capability of the species distribution model. Areas predicted to have higher intensity of use by our model can be used to focus efforts of continued protection of areas with frequently occupied and productive nest sites, and conversely, identify areas where protection of nest sites is likely to have few conservation benefits.

Alaska↗
USGS2023

Monitoring Avian Productivity and Survivorship (MAPS) 6-year summary, Naval Outlying Landing Field, Imperial Beach, southwestern San Diego County, California, 2014–20

Executive Summary From 2014 to 2020, a Monitoring Avian Productivity and Survivorship (MAPS) banding station (station) was operated at the Naval Outlying Landing Field (NOLF), Imperial Beach, in southwestern San Diego County, California. The station was established as part of a long-term monitoring program of Neotropical migratory bird populations on NOLF and helps Naval Base Coronado (NOLF is a component) meet the goals and objectives of the Department of Defense Partners in Flight program and the Birds and Migratory Birds Management Strategies of the Naval Base Coronado Integrated Natural Resources Management Plan. The station was established in 2009 and has been in operation during the spring and summer since 2009 except for 2016 when it was not funded. The station was operated by AMEC Earth and Environmental, Inc., from 2009 to 2011, by the U.S. Geological Survey from 2012 to 2015, the San Diego Natural History Museum in 2017, and the U.S. Geological Survey again from 2018 to 2023. This report synthesizes results from 2014 to 2020. A prior report presents summaries and analyses from 2009 to 2013. The banding station at NOLF was operated according to the standard MAPS protocol with some exceptions. Ten mist nets used to capture birds were erected in fixed locations that remained consistent between and within years, with few minor relocations. Nets were open for 6 hours per day, once every 10 days (a netting period) for 13 netting periods starting April 1 each year. Occasionally, poor weather conditions (for example, rain, wind, or excessive heat) prevented net operation or forced nets to be closed early (or, rarely, late). Nets were checked periodically throughout the day and birds were removed, processed (leg bands affixed, measurements recorded), and released. From 2014 to 2020, we had 3,543 captures (including initial captures and recaptures) of a maximum of 3,264 year-unique captures (543±143 year-unique captures [the total number of individual birds captured for the first time each year]). The count of year-unique captures included 2,702 newly banded birds, 258 individuals that were recaptured from previous years, and 304 birds that were released unbanded (218 hummingbirds and 86 other birds that were intentionally released unbanded [game birds, and so forth] or escaped before banding). Individuals of 68 species were captured, 39 of which breed at or in the immediate vicinity of the MAPS banding station. Bird capture rate averaged 43±30 captures per day (corrected to account for variation in effort) for all years (range 7–163 effort-corrected captures per day) and species richness per year averaged 43±4. Bushtit ( Psaltriparus minimus ) was the most abundant species captured, followed by Orange-crowned Warbler ( Leiothlypis celata ), Wilson’s Warbler ( Cardellina pusilla ), House Finch ( Haemorhous mexicanus ), Song Sparrow ( Melospiza melodia ), and Common Yellowthroat ( Geothlypis trichas ). The mean adult sex ratio of all species combined across all years was 54:46 male:female. Adults averaged 73±12 percent of known age captures per year (range 59–94 percent), and juveniles averaged 27±12 percent (range 6–41 percent). Nineteen sensitive species were detected at NOLF (12 captured and 7 observed only). During 2014–20, we captured one State and federally endangered species, Least Bell’s Vireo ( Vireo bellii pusillus ); one federally threatened species, California Gnatcatcher ( Polioptila californica ); one State endangered species, Willow Flycatcher ( Empidonax traillii ); and two State species of concern, Yellow-breasted Chat ( Icteria virens ) and Yellow Warbler ( Setophaga petechia ). One additional State species of concern, Northern Harrier ( Circus hudsonius ), was observed at the MAPS banding station but not captured. Peregrine Falcon ( Falco peregrinus ) and White-tailed Kite ( Elanus leucurus ), California State fully protected species, also were observed at the MAPS banding station. Seven federal bird species of conservation concern—Calliope Hummingbird ( Selasphorus calliope ), Rufous Hummingbird ( Selasphorus rufus ), Allen’s Hummingbird ( Selasphorus sasin ), Nuttall’s Woodpecker ( Dryobates nuttallii ), Wrentit ( Chamaea fasciata ), California Thrasher ( Toxostoma redivivum ), and Lawrence’s Goldfinch ( Spinus lawrencei )—also were captured, and four additional federal bird species of conservation concern—Willet ( Tringa semipalmata ), Western Gull ( Larus occidentalis ), California Gull ( Larus californicus ), and Bullock’s Oriole ( Icterus bullockii )—were observed but not captured. Local population trends varied among species and years. From 2012 to 2019, year-round residents Bushtit, Song Sparrow, and Common Yellowthroat significantly decreased, whereas the migrant Least Bell’s Vireo increased. The total number of captures for all species except Least Bell’s Vireo was lowest in 2017, corresponding to the habitat damage caused by Kuroshio shot hole borer beetle ( Euwallacea kuroshio ) in the Tijuana River Valley. Annual productivity and annual adult survival were calculated for seven breeding species based on criteria used by the Institute for Bird Populations (Least Bell’s Vireo, Bushtit, Wrentit, House Wren [ Troglodytes aedon ], Song Sparrow, Orange-crowned Warbler, and Common Yellowthroat). Productivity was highest for most species in 2010 and 2019, years with high precipitation, and lowest in 2014 and 2018, years with low precipitation. Song Sparrow demonstrated the highest productivity among species and Least Bell’s Vireo had the lowest productivity. Annual adult survival was generally high from 2011 to 2012 and from 2018 to 2019. Bushtit had higher annual survival with lower late winter precipitation. Either temperature or precipitation was associated with productivity for all species except Wrentit, and with survival for all species except Least Bell’s Vireo and Common Yellowthroat. For most species, productivity was positively associated with precipitation, and both productivity and survival were negatively associated with temperature. Other studies have found that higher temperatures led to increased predation by snakes and birds and also increased vector-borne disease transmission, such as West Nile virus. Predicted regional increases in temperature over the next 30 years will likely affect the demographics of these species. The Song Sparrow population increased with higher breeding productivity during the previous year, and the Bushtit population increased with higher annual survival and higher productivity during the previous year. Aside from a possible positive association between survivorship and Common Yellowthroat population growth, productivity and survival rates did not appear to influence population change for other focal species.

California↗
USGS2016

An international borderland of concern: Conservation of biodiversity in the Lower Rio Grande Valley

The Lower Rio Grande Valley (LRGV) of southern Texas is located on the United States-Mexico borderland and represents a 240-kilometer (150-mile) linear stretch that ends at the Gulf of Mexico. The LRGV represents a unique transition between temperate and tropical conditions and, as such, sustains an exceptionally high diversity of plants and animals—some of them found in few, or no other, places in the United States. Examples include Leopardus pardalis albescens (northern ocelot) and Falco femoralis septentrionalis (northern aplomado falcon)—both endangered in the United States and emblematic of the LRGV. The U.S. Fish and Wildlife Service (USFWS) manages three national wildlife refuges (Santa Ana, Lower Rio Grande Valley, and Laguna Atascosa) that together make up the South Texas Refuge Complex, which actively conserves biodiversity in about 76,006 hectares (187,815.5 acres) of native riparian and upland habitats in the LRGV. These diminished habitats harbor many rare, threatened, and endangered species. This report updates the widely used 1988 USFWS biological report titled “Tamaulipan Brushland of the Lower Rio Grande Valley of South Texas: Description, Human Impacts, and Management Options” by synthesizing nearly 400 peer-reviewed scientific publications that have resulted from biological and sociological research conducted specifically in the four Texas counties of the LRGV in the past nearly 30 years. This report has three goals: (1) synthesize scientific insights gained since 1988 related to the biology and management of the LRGV and its unique biota, focusing on flora and fauna of greatest conservation concern; (2) update ongoing challenges facing Federal and State agencies and organizations that focus on conservation or key natural resources in the LRGV; and (3) redefine conservation opportunities and land-acquisition strategies that are feasible and appropriate today, given the many new and expanding constraints that challenge conservation activities in the LRGV. The LRGV faces every contemporary conservation challenge of the 21st century, but ongoing human population growth and its associated demands, international border issues, and oil, gas, and alternative energy development dominate impacts that affect conservation in the LRGV. Continued careful syntheses of existing and future information collected in the LRGV are needed on many biological and sociological topics to guide conservation activities. Quick response will no doubt be necessary to face contemporary and difficult-to-predict challenges such as climate change, diminished water availability and quality, spread of invasive species, and habitat loss and fragmentation. Complexities of a guarded international borderland add pressure to small patches of native habitat that remain in many places of the LRGV, particularly along the Rio Grande. Large connected corridors of restored native habitat could be the best option to maintain, and even enhance, the exceptional biodiversity of the LRGV in the face of exceptional human demand.

Texas↗
USGS2009

Unusual raptor nests around the world

From surveys in many countries, we report raptors using unusual nesting materials (e.g., paper money, rags, metal, antlers, and large bones) and unusual nesting situations. For example, we documented nests of Steppe Eagles Aquila nipalensis and Upland Buzzards Buteo hemilasius on the ground beside well-traveled roads, Saker Falcon Falco cherrug eyries in attics and a cistern, and Osprey Pandion haliaetus nests on the masts of boats and on a suspended automobile. Other records include a Golden Eagle A. chrysaetos nest 7.0 m in height, believed to be the tallest nest ever described, and, for the same species, we report nesting in rudimentary nests. Some nest sites are within a few meters of known predators or competitors. These unusual observations may be important in revealing the plasticity of a species' behavioral repertoire. ?? 2009 The Raptor Research Foundation, Inc.

Journal of Raptor Research↗
USGS2010

Detection probability of cliff-nesting raptors during helicopter and fixed-wing aircraft surveys in western Alaska

We conducted repeated aerial surveys for breeding cliff-nesting raptors on the Yukon Delta National Wildlife Refuge (YDNWR) in western Alaska to estimate detection probabilities of Gyrfalcons (Falco rusticolus), Golden Eagles (Aquila chrysaetos), Rough-legged Hawks (Buteo lagopus), and also Common Ravens (Corvus corax). Using the program PRESENCE, we modeled detection histories of each species based on single species occupancy modeling. We used different observers during four helicopter replicate surveys in the Kilbuck Mountains and five fixed-wing replicate surveys in the Ingakslugwat Hills near Bethel, AK. During helicopter surveys, Gyrfalcons had the highest detection probability estimate (p^;p^ 0.79; SE 0.05), followed by Golden Eagles (p^=0.68; SE 0.05), Common Ravens (p^=0.45; SE 0.17), and Rough-legged Hawks (p^=0.10; SE 0.11). Detection probabilities from fixed-wing aircraft in the Ingakslugwat Hills were similar to those from the helicopter in the Kilbuck Mountains for Gyrfalcons and Golden Eagles, but were higher for Common Ravens (p^=0.85; SE 0.06) and Rough-legged Hawks (p^=0.42; SE 0.07). Fixed-wing aircraft provided detection probability estimates and SEs in the Ingakslugwat Hills similar to or better than those from helicopter surveys in the Kilbucks and should be considered for future cliff-nesting raptor surveys where safe, low-altitude flight is possible. Overall, detection probability varied by observer experience and in some cases, by study area/aircraft type.

Alaska↗
USGS2011

Sex-related differences in habitat associations of wintering American Kestrels in California's Central Valley

We used roadside survey data collected from 19 routes over three consecutive winters from 2007–08 to 2009–10 to compare habitat associations of male and female American Kestrels ( Falco sparverius ) in the Central Valley of California to determine if segregation by sex was evident across this region. As a species, American Kestrels showed positive associations with alfalfa and other forage crops like hay and winter wheat, as well as grassland, irrigated pasture, and rice. Habitat associations of females were similar, with female densities in all these habitats except rice significantly higher than average. Male American Kestrels showed a positive association only with grassland and were present at densities well below those of females in alfalfa, other forage crops, and grassland. Males were present in higher densities than females in most habitats with negative associations for the species, such as orchards, urbanized areas, and oak savannah. The ratio of females to males for each route was positively correlated with the overall density of American Kestrels on that route. Our findings that females seem to occupy higher quality habitats in winter are consistent with observations from elsewhere in North America.

California↗
USGS2021

Food habits of American Kestrels in the Southern High Plains of Texas

The American Kestrel ( Falco sparverius ) is in general decline across its North American distribution. In contrast to widespread patterns of decline, kestrel populations appear stable in the southern Great Plains region. Historically, this region had a very low occurrence of kestrels, and their current abundance is highly likely due to vegetation and structures associated with settlement by people of European descent. To determine prey use by breeding kestrels, we placed motion-activated video cameras at preexisting kestrel nest boxes located in the Southern High Plains in 2017. We recorded over 4200 prey deliveries during 1748 hr of observation at five nests over the 4-wk brood-rearing period. On basis of frequency, these deliveries were dominated by reptiles (74.8%), with invertebrates (18.2%), mammals (4.4%), birds (2.9%), and unidentified (1.2%) prey used to lesser extents. Prey delivery rates were high relative to other studies; across the brood-rearing period we recorded an average of 2.3 deliveries/hr, equating to an average of 0.49 deliveries and 3.85 g of prey/nestling/hr. Because invertebrates dominate the diet reported in most kestrel food habit studies, the volume of reptiles captured as prey was unexpected. Even more unanticipated was the number of large prey captured, including juvenile eastern cottontails ( Sylvilagus floridanus ) and ground squirrels ( Ictidomys tridecemlineatus , Xerospermophilus spilosoma ). We suspect the proportion of vertebrate prey captured during the nesting season may explain the local high rates of nesting success and number of young fledged.

Texas↗
USGS2023

Seasonal abundance and habitat associations of American Kestrels on the Southern High Plains of Texas

American Kestrel ( Falco sparverius ) populations are generally declining across the species' North American distribution but the population in the Southern High Plains region currently appears to be stable. Historical evidence suggests the region formerly had a low abundance of kestrels, and that their current numbers are due to landscape changes associated with European settlement. We conducted monthly surveys for American Kestrels across 2 yr to estimate seasonal densities and identify land cover associations in the Southern High Plains of Texas. We found an overall estimated density of 0.99 birds/km 2 (95% CI = 0.406, 1.582) across the 2-yr period, with seasonal estimated densities highest in autumn and winter (0.92–2.53/ km 2 ), and lowest in spring (0.49–0.67/km 2 ). Whereas other studies have found that temperature influenced detection of wintering kestrels, we found an interaction of drought conditions and snow most strongly influenced the number of kestrels in our study area. Kestrels largely used land cover types in proportion to availability but there was some evidence of seasonal shifts. Generally, they tended to avoid cotton fields and sometimes selected for areas with woodlots, abandoned or occupied houses, and barns, all of which likely provided nesting and roosting opportunities. Our study provides the first contemporary assessment of seasonal abundance and habitat associations of American Kestrels in the Southern High Plains, where their presence and abundance has been unintentionally facilitated by landscape changes following settlement. We provide a baseline for population monitoring and studies assessing response to additional landscape changes (e.g., development of wind energy facilities) and a changing climate.

Journal of Raptor Research↗